First off, servos, no. You want brushless dc motors with speed controllers.
So, you want it to auto balance itself but you control it?
And the weight it can carry safely will depend on how strong the motors are/how much the whole thing weighs itself.
By the sounds of things, you haven't done much research?
You will need to do LOTS for this kind of project, it is a very complicated project, just to get it flying is hard. But if you can do it, great!